This invention relates to wake-up circuits, and more particularly, to a wake-up circuit utilizing a voltage decay detector and a signal generator to detect change in a power supply potential level and to switch a device from a powered-down state to an active state when such change is detected.
With certain electronic devices there are many functions which may need to be performed at initial power-on, such as self-testing, clearing data from memory and restoring elements to a know state. Thus many types of electronic devices include a power-on reset (POR) circuit. A POR circuit generally detects when power is applied to a device and then issues a reset pulse or signal which is used to initiate the above functions.
Many electronic devices, such as low power devices, utilize a zero power stand-by mode in which parts of the device not needed during normal operation are shut off to conserve power consumption by the device. Consequently, some internal POR circuits have been made to shut off and thereby draw no current once they have properly reset a device after a power-up sequence has been performed.
One method of operation used by current POR circuits during the power-up of an electronic device has the POR circuit generating a reset signal for the electronic device during the power-up until the operating voltage of the electronic device reaches a certain threshold. Once the threshold is reached, the POR circuit switches to the stand-by or powered-down state. The POR circuit will then remain in the powered-down state until the operating voltage of the electronic device has returned to zero volts.
However, a problem arises when the operating voltage of the electronic device fluctuates and decays below the threshold but does not decay completely to zero volts. If this occurs, any subsequent rise in the operating voltage will not trigger the POR circuit to reset the electronic device, thereby placing the electronic device in an unknown state.
Past and current POR circuit technologies that monitor the operating voltage for in-tolerance conditions, monitor the operating voltage at all times, thereby utilizing ""stand-by current. This creates an additional problem with low powered devices, because, as described above, for low power devices minimum power consumption is often critical.
Therefore, a POR circuit is needed having a powered-down state that can be activated anytime the operating voltage is low enough for an incorrect operation of the electronic device to result and still be able to monitor the threshold voltage with minimum power consumption.
The present invention overcomes the above identified problems as well as other shortcomings and deficiencies of existing technologies by providing circuitry to detect change in a power supply potential level and to switch a power-on reset circuit from a powered-down state to an active state, while maintaining minimum power consumption.
Accordingly, it is an object of the present invention to provide a wake-up circuit having a voltage decay detector for monitoring change in a power supply potential level, and having a signal generator to generate a pulse to switch a device from a powered-down state to an active state when change in the power supply potential level is detected.
It is a further object of the present invention to provide an initializer having a power-on reset circuit that switches between a powered-down state and an active state when change in a power supply potential level is detected.
In accordance with the above and other objects there is provided a wake-up circuit that is operable in response to change in a power supply potential level, that generates a wake-up signal to switch the state of a component from a stand-by state to an active state. The wake-up circuit includes a voltage decay detector that detects change in the power supply potential level and includes a signal generator that generates the wake-up signal used switch the state of the component from the stand-by state to the active state when change in the power supply potential level is detected. The wake-up circuit has no appreciable stand-by power.
There is further provided an initializer that is operable in response to change in a power supply potential level, that generates an initialize signal to initialize a circuit to a selected state. The initializer includes a power-on reset circuit that generates the initialize signal and is switchable between a stand-by state and an active state. The initializer also includes a detector that detects the change in the power supply potential level and includes a signal generator that generates a wake-up signal when change in the power supply potential level is detected. The wake-up signal switches the power-on reset from the stand-by state to the active state.